The application of camshaft position sensors in four cycle internal combustion engine control is known generally in the engine control art. Camshaft position sensors and the hardware and software used to process camshaft position sensor signals typically provide information on engine absolute angular position for synchronization of relative position sensor signals, such as signals output from engine crankshaft position sensors. The relative engine position signals are considered "synchronized" when they are properly interpreted to indicate occurrence of individual engine cylinder events.
The camshaft position sensor typically includes a variable reluctance or hall effect sensor positioned to sense passage of a single tooth or notch on the camshaft. Unlike the engine output shaft, the camshaft rotates once for each engine cycle, and thus the sensed passage indicates absolute engine angular position. The cost of the camshaft position sensor and its associated signal processing hardware and software is significant. Furthermore, engine performance may be significantly reduced if the sensor or its associated hardware or software fails to operate properly. For example, cam sensing faults may lead to significant fuel injection timing error, reducing engine performance and increasing engine emissions.
Pursuant to ambitious engine emissions reduction goals, an increasing number of engine diagnostic systems include advanced cylinder misfire diagnostics which attempt to detect engine misfire conditions and to identify the misfiring cylinder. As such diagnostics may already be present on many automotive vehicles, and as such diagnostics detect individual cylinder misfire conditions during combustion events, and as combustion events of individual cylinders may be used to determine absolute engine angular position, it would be desirable to adapt such misfire detection systems to supplant or at least complement camshaft position sensing approaches for use in determining absolute engine angular position.